Removal of rare-earth elements from complex aqueous solutions using a microporous niobium-iron silicate: From optimisation to simulated e-waste applications

Abstract

The increasing demand for rare-earth elements (REEs), driven by technological advancements and the global transition towards green energy, has raised concerns over their sustainable supply and environmental impacts associated with their extraction and processing. Industrial effluents and electronic waste recycling activities can generate aqueous streams with high REEs concentrations, necessitating the development of efficient remediation and recovery strategies. This study provides a systematic evaluation of the microporous niobium-iron silicate Na_2.9(Nb_1.55Fe_0.45)Si₂O₁₀·xH₂O for the removal of REEs from mineral water and simulated electronic waste leachates (permanent magnets and lamp phosphor waste), extending previous investigations performed under simplified experimental conditions. The effects of pH, REEs initial concentration, and sorbent dosage were systematically analyzed using response surface methodology based on a Box–Behnken Design. Using this approach, optimal conditions were identified at pH 4.2, a sorbent dosage of 179 mg/L, and an initial REEs concentration of 1.8 μmol/L, under which removal efficiencies of over 80% for neodymium (Nd) and 60% for yttrium (Y) were achieved after 6 h of contact time. Additional experiments with synthetic waste solutions confirmed the sorbent’s high efficiency, reaching removal rates above 95% for Nd and Y at initial concentrations of 5 and 10 μmol/L. Kinetic modelling showed that the uptake profiles were best described by the Elovich model for Nd and the pseudo-second-order model for Y. These results are consistent with the involvement of surface interactions and possible ion-exchange processes, although they do not provide direct proof of a specific sorption mechanism. These findings demonstrate the potential applicability of the material for REEs removal from complex wastewaters, offering a pathway toward more sustainable critical raw material management.